Alterations in Home Range Space Use over a Multi-Year Study of Nassau Grouper (Epinephelus striatus)

SIERRA STEVENS-MCGEEVER¹, BRICE SEMMENS¹, CHRISTY PATTENGILL- SEMMENS², SCOTT HEPPELL³, PHILLIPPE BUSH⁴ , BRADLEY JOHNSON⁴ and CROY MCCOY⁴

1. Scripps Institution of Oceanography La Jolla, Ca 2. Reef Environmental Education Foundation 3. Oregon State University 4. Cayman Islands Department of the Environment

ABSTRACT
Characterizing long-term movement patterns and space use is vital to developing a robust understanding of spatial ecology. While short-term tracking is informative regarding daily movement patterns, long-term data provide insight into the stability of these spatial use patterns. In this study, we examine the variation in home range space use of Nassau grouper (Epinephelus striatus). Using acoustic telemetry, we monitored the movements of Nassau grouper in the Cayman Islands by examining the frequency of detections at hydrophones located within the home range of tagged fish. Changes in the number of detections through time signified alterations in the habitat occupied by Nassau groupers, suggesting that these fish may have larger home ranges than previously thought, or that Nassau groupers exhibit home range drift. This idea is supported by data from depth-coded tags, where two of our study fish shifted the depth of their home range. We used a time series analysis (Fast Fourier Transformation (FFT)) to identify cyclical patterns in frequency of tag detections. The FFT analysis showed marked peaks in the number of detections per day at 24-hour cycles. Evidence for long-term shifts in home ranges could have implications for the management of this endangered species by changing our understanding regarding the space required for effective spatial management. Fish in this study showed distinctly different depth use patterns when compared to the only other long-term acoustic study of this species, suggesting that movement patterns and space use of this species may depend greatly on local habitat characteristics and oceanic conditions.

KEYWORDS: Spatial ecology, Grouper, Epinephelus striatus, Home Range, Acoustic Telemetry